Method and apparatus for annealing metal charges



Aug. 15, 1939 J. R. TAYLOR 2,169,621

METHOD AND APPARATUS FOR ANNEALING METAL cameras Filed Oct. 9, 1.937 3Sheets-Sheet 1 N M flylNVENToR.

1L2 ATTORNEYS.

5, 1939 J. R. TAYLOR 2,169,621

METHOD AND APPARATUS FOR ANNEALING METAL CHARGES ALL; A TTORNEYS.

Aug. 15; 1939 J. R. TAYLOR METHOD AND APPARATUS FOR ANNEALING METALCHARGES Filed Oct. 9, 1937 3 Sheets-Sheet 5 INVENTOR.- ;Z%s@ 44;,ATTORNEYS.

Patented .Aug. 15, 1939 UNITED STATES PATENT oFF cE METHOD AND APPARATUSFOR ANNEALING METAL CHARGES John R. Taylor, Natrona, Pa., assignor toAllegheny Steel Company, a corporation of Pennsylvania ApplicationOctober 9, 1937, Serial No. 168,233

9 Claims.

My present invention relates to the art of annealing charges of metalarticles, for example, metal sheets, and more particularly concerns aprocedure and an apparatus whereby such charges can be uniformlyannealed or heat treated in a reduced period of time.

to as the inner cover, and a removable refrectory heat-insulating coveris placed over the inner cover and spaced therefrom. This refractoryheat-insulating cover will be herein after referred to as the outercover. Ordinarily, means is provided in the outer cover for applyingheat between the outer and inner covers for the purpose of bringing thecharge to annealing tempe'rature and inasmuch as it is the outer coverwhich must be removed from time to time, certain disadvantages haveresulted which are well recognizedin this industry. For example, theouter covers have generally been heavy and cumbersome as well asexpensive, requiring heavy and hazardous crane lifting. In moving theouter cover it has always been necessary to disconnect the gas linesassociated therewith and this has resulted indifiiculty and delay.

In prior furnaces constructed. along the foregoing lines it has beenfound that relatively poor fuel economy is secured and that it has beenimpossible actually to secure uniform annealing or heating. Tests madewith thermo-couples inserted at various locations in the metal chargehave shown temperature variations as great as 50 to 60 degrees F. anddue to the natural propensity ofheat to rise rapidly, the top of thecharge is usually hotter than other portions thereof and if theannealing time is prolonged to raise the most difliculty accessibleparts of the charge to the desired temperature, then some portionsof-the charge are always found to be over-anhealed. If this is not donethen some portions will be over-annealed and some under-annealed.

Other disadvantages are recognized, such as lack of satisfactoryflatness where metal sheets or the like are annealed and the liabilityto explosion dueto, the disturbing of,the gas con.- nections.

It is accordingly one of the objects of w my present invention to carryout annealing under such cqnditions as I? av d t e i i mt es anddisadvantages hitherto encountered and to accomplish annealingoperations in a reduced period of time with greatly enhancedeffectiveness.

' Another object of my invention resides in annealing stacks of sheetsor other metal articles with a condition of uniformity of temperaturethroughout the charge not heretofore obtainable and t the same time toaccomplish this in a shorter period of time and with greater fueleconomy as compared with prior practice.

Other and ancillary objects and advantages reside in the provision of anouter furnace cover which is light and easy to handle and which is freefrom obstructing connections of any sort; the production of a furnacewherein the base is permanent and is provided with permanent gasconnections, thereby eliminating those hazards and inconveniencesresulting from the use of portable gas connections, andin general theprovision of a new procedure and a new furnace as well as certain dtails thereof which will accom-. plish the objec and advantages hereinoutlined. In the accompanying drawings, wherein like numerals designatecorresponding parts:

Figure 1 is a transverse section through a furnace embodying the presentinvention;

Fig. 2 is a view partly in section and partly in perspective of afurnace essentially the same as Fig. 1 but provided with vent'stacks;

Fig. 3 is a perspective view of the heating system of Figs. 1 and 2; and

Fig. 4 is a fragmentary modified heating system.

I have discovered that a much improved annealing furnace and procedurecan be produced by applying a gaseous heating medium through the base ofthe furnace and transmitting heat by conduction first to the bottom ofthe charge while the heating medium is' at its maximum temperature. Thenthe heating medium is caused to pass between the inner and outer coversand to impart heat to the sides and top of the charge perspective viewof a but out of direct contact with the charge, thus resulting in newqualities of uniformity of annealing and reduction of the duration ofthe annealing cycle.

One mode of constructing a furnace to satisfy these requirements isillustrated in Figures 1 and 3am! in those figures it will be apparentthat the furnace consists of three main parts, a base'lll, an outercover H and an inner cover l2. The base I0 is built up of suitablerefractories l3 within a structural steel shell M, the base resting upona concrete or other flooring ii. To this shell suitable structural steelbeams I6 dered) insulating refractory H, such as Sil-ocel, and thisarrangement, I have found, cuts down heat losses due to radiation and atthe same time allows for expansion.

Passing transversely through the refractory base It is a series of tubesl8 through which heatingmedium is passed. Each tube I8 is made up of arefractory material having a high rate of heat transfer, such ascarborundum, and is preferably composed of a number of sections suitablysecured together to form a closed heating tube or conduit. These tubesor conduits may, however, be made of any other satisfactory material ofhigh heat transfer properties which will withstand the temperatures andother conditions of operation and suitable metals or alloys may be usedfor this purpose.

From Figure 1 especially it will be apparent that the tubes I! extendfrom one side of the base nearly to the opposite side and that theyterminate in upwardly extending elbow portions I9 which communicate withthe space or chamber 23 between outer cover II and inner cover II. FromFig. 3 in particular, it will be understood that adjacent tubes areoppositely disposed, that is, the tubes i3 alternately start at oppositesides of the base. andaiternately discharge via the upwardly extendingelbow-portions is into the space 20 but at opposite sides of thefurnace. The tubes 18 are alternately fired from opposite sides of thebase and for this purpose I provide a manifold 2| alongeach sideprovided with retractible gas burners 22 in the usual manner understoodin this art.

It will be further noted from Figure 1 that superjacent. the tubes l8there are two courses of refractory 23 and 24 forming a central raisedor pier portion for the base Ill. The inner cover I! rests indepressions or recesses 25 at either sideof the central pier and asuitable seal is made, as by sand 26, to exclude air in known manner,Likewise, the upper outer edges of the base i0-are cut away as at 21 andthe spaces thereby produced are filled with sand go for making a sealwith thedownwardly extending flanges 29 of the outer cover H. Ihavefound, however, that due to the porosity of all refrac' torles someleakage of air or gas inevitably infiltrates within inner cover' I!particularly while the charge is cooling, since the lowering of thetemperature creates a sucking effect probably due to the formation of apartial vacuum within the cover which draws in air. This'isobjectionable in connection with the inner cover since air or oxygenfinding its way thereinto will cause oxida tion and discoloration of thehot metal charge. To prevent the inherent porosity of the refractorymaterials-from enabling air or the like to gain access within the innercover I provide the metal plate 30 which effectively seals the chamberswithin the covers from such effect. This metal plate 30 is shaped asshown in section in Figure 1 and is composed of any suitable metal whichwill withstand the conditions of operation of the furnace and which isimpervious or substantially impervious to the passage of air or gasestherethrcugh except, of course, that the plate is provided with rows ofapertures 3i in each side thereof in order not to interfere with'the'upwardly extending tube elbow p rtions l9 which discharge heatingmedium (hot gases) between the two covers.

As stated, the inner metal cover l2 rests within the recesses ordepressions 25 in the base ill. The plate 30 is shaped to correspond tothese recesses and a sand seal or other suitable seal is provided atsuch points. Thus heating medium discharged from elbows I9 is maintainedout of direct contact with the charge of metal 32 without objectionablyimpeding or obstructing the transmission of heat from ,the medium to thecharge. The presence of the inner cover permits removal of the outercover after heating is discontinued and thus enables one outer cover tobe used with a plurality of bases asls understood in this art.

Outer cover II is madeof suitable refractory material 33 with an archedroof 34 disposed within a structural metal shell 35, the arched roof 34being provided with one or more vents 36 so that the heating medium maypass therethrough after it has carried out its purpose of heating thecharge 32. It will be noted that the removable cover is of comparativelylight weight and great portability, particularly as compared with priorart outer covers, and this not only cuts down the cost of theseremovable covers and'reduces crane lifting operations to a minimum butmakes it easy to utilize a single removable cover 'for a plurality ofpermanent stationary bases.

At the same time the removable cover has no fuel or other connectionsand hence the removal thereof is greatly facilitated.

A relatively thick metal plate 31 which may be, for example, in theneighborhood of 1 inches thick-is placed upon that portion of metalplate 30 which rests upon the refractories 23, 24 and it is this thickplate 31 which receives the charge of material as is apparent.

It is recognized by annealers that the central lower portion of thecharge, particularly when the charge consistsof flat sheets, is the mostdifficult, to heat and that ideal conditions would result if thisportion of the charge were a few 1 degrees hotter than the balance ofthe charge and could be heated first to the required temperature sinceit is relatively inaccessible to the heating medium. The relativeinaccessibility of such to the heating medium ordinarily results inunder-annealing this portion of the charge and if the armeallngtemperature is so high or the annealing period so prolonged as to bringthis porton up to proper temperature then the top and sides of thecharge are inevitably overannealed. This inaccessible charge portion isdemarked by the line indicated at 33. It will be understood from Fig. 1in view of the arrows placed thereon that as heating medium is passedthrough tubes l8 its first and full effect thereof is transmitted tothis inaccessible charge portion 38 through the refractories and metalforming the pier and the effect of this is to bring the inaccessiblecharge portion up to temperature first and rapidly while the heatingmedium is at its highest temperature. This heating effect substantiallyoccurs through conduction, as will be understood.

Due to the fact that alternate heating tubes are oppositely fired, thetemperature of the bottom of the charge is readily equalized. After theheating medium passes through the tubes it turns up wardly through thetube elbows i9 and passes into the chamber 20 between the covers ii andi2. As it passes through this chamber it is deflected to the top of thecharge by the arched roof and eventually passes from the furnace viavent 36 but during this. passage. through the chamber 20 it transmitsheat both to the inner cover I! and toing of the sides and top of thecharge and causes quick and deep penetration of the heat to the interiorof the charge. This I have found gives an unusual uniformity of heatingand annealing and tests made by me in this connection have shown -amaximum diflerential of not over about 20 degre'es F. between variousportions of the charge as compared with common 50-60 degree F.differences'in prior practice. Thus, even on the basis of uniformity ofheating alone, my present invention is a great improvement over priorpractice.

By permitting fresh air at room temperature to pass through the tubes I8I have also found that I can cool the charge uniformly and in amaterially reduced period of time, thus cutting down the entireannealing cycle involving the heating and cooling operations. To do thisI may retract the burners whichare ordinarily spring pressed toward theopen tube ends in conven-- tional manner and the conditions are suchthat this will cause fresh air to be sucked into the tubes l8 and intochamber 20 and if I so desire I may enhance this effect by admittingsuch air under forced draft, but in the-latter case retracting of theburners is not required.

I have further discovered that this construction and procedure forcarrying out annealing gives me at least a 20 to 60 per cent betterfuel, economy. For example, where in a conventional annealing furnace Ihave found that approximately 1576 cubic feet of gas'were required pernet ton of charge, under the same conditions my annealing furnaceconsumed approximately only 1194 cubic feet of gas per net ton ofcharge, an improvement of the order of per cent. In operating a furnacein accordance with my present invention I-have found that the firingtime and the heat treating cycle are reduced at least 10 to 50 per centas compared with prior operations in conventiona furnaces. Where thecharge consists of fiat metal sheets, plates or the like theannealedproduct produced by me in accordance with this invention ischaracterized by much impr d flatness in contradistinction to priorpractice ficient in that quality due to distortion, warping etc., whichmay be explained at least in part by the non-uniform annealing thereof.r

While in Figures 1 and 3 I have illustrated a preferred form of thepresent invention which is eminently satisfactory, Imay make certainvari ations thereof such as indicated in Figure 2. In the latter figurethe parts are substantially the same as in Figs. 1 and 3, as indicatedby the use of corresponding numerals, but in the form of the inventionillustrated in Figure 2 I have employed auxiliary chimneys or stacks 33,the lower ends of which respectively communicate with the elbow'portions IQ of tubes I. As will be understood from Fig. 2, each chimneyor stack 39 is composed of an upper cylindrical portion formed ofrefractory or metal of suitable composition and a lower somewhatbell-shaped portion so as to fit over the elbow portions l9 aforesaid.Suitable braces or supports 40 are provided to maintain chimneys orstacks 39 inproper association I with the remainder of the structure andthese chimneys or stacks extend through the roof of here the annealedsheets or plates are dethe furnace, as shown, and exhaust to the atmos-'phere. In utilizing this form of the invention the heating medium, suchas hot gases, passes as before, through tubes I8 and elbows l9 but theninstead of discharging into the space 20 between In order to-prevent thenatural propensity of heat to rise to carry off the heating medium toorapidly for efficient operation, I provide each chimney or stack 39 witha core-buster which is made up of a chain or the like 4! to which areafixed in spaced relationship a series of discs or the like 42 which arecomposed of suitable refractory or metal and which have a maximumdiameter somewhat less than the internal diameter of the chimneys orstacks. Thus the upward flow of heat is retarded and checked to thatextent found necessary or desirable to make the most efiicient use ofthe heating medium for this purpose. In such case it is not necessary toprovide vents in the arched roof of the furnace, as shown at 38 in Fig.1, and where the bell-shaped lower ends of the chimneys or stacks 39meet the elbows IS a suitable sealing is effected, such as by sand orany other recognized sealing medium.

I am not limited to the precise arrangement of tubes l8 as utilized inFigures 1 to 3, inclusive, because I have found that I can vary thearrangement and disposition of such tubes without loss in effectivenessand under some conditions, i. e.,

.for some types of metal charges, even improved results are secured bysuch tube variation. In Figure 4 the gas manifolds 2| are provided withthe retractable burners 22 as before and tubes l8 are alternately firedfrom opposite sides of the .base but each tube l8, instead ofterminating adjacent the opposite side of the base in which it islocated, returns to the same side and there discharges via upwardlyextending elbows l9 either into the space 20 (as per Fig. 1) or into thechimneys or stacks 33 (as per Fig. 2). While in Fig. 4 I have shown thetubes I8- as being U- shaped, they may be provided with any type ofreturn bend, such as a horse-shoe bend, a hairpin bend or any othersuitable arrangement and if I so desire I may provide each tube withmultiple bends making them S-shaped or any other form, depending uponthe resultsto be accomplished in a given case and the termini of suchtubes may be at the same or the opposite side as the starting pointsthereof.

While I have particlularly described the invention in connection with acharge of metal sheets, this is for exemplary purposes only, and it isto be understood that the furnace and the procedure herein described andclaimed is equally applicable to the treatment of all ferrous andnon-ferrous materials in any form whatsoever. Among these forms I havefound that the invention is suitable for the heat treatment or annealingof sheets, plates, strips, bars, rods, coils, castings and variousmiscellaneous shapes.

Other and further modifications, omissions, substitutions andalterations may be made in my present invention, as will be understoodby those skilled in this art, and all such are deemed to be a part of mypresent invention and are intended to be covered by the appended claims.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patout is: a

1. Apparatus for uniformly and rapidly annealing a charge of metalsheets comprising a base, a removable heat-insulating cover and anair-excluding cover within and spaced from said heat-insulating cover, ametal sealing plate disposed upon said base and upon which said air;excluding cover rests, and means for sealing said covers to exclude airfrom within them, said base being provided with heating ducts whichterminate in elbow portions disposed between said covers.

2. An annealing furnace comprising a refractory base traversed bytubular heating ducts composed of material having a high rate of heattransfer, a removable heat-insulating cover and an inner spacedair-excluding cover, a sealing plate disposed upon said base and uponwhich said air-excluding cover rests, a seal between saidheat-insulating cover and said base and between said air-excluding coverand said plate, means for passing heating gases through said base ductsand thence upwardly between said covers and means for venting the spentgases to the atmosphere.

3. A method of annealing a metal charge on a pier confined and sealedwithin an inner cover which is enclosed within a spaced outer covercomprising the steps of conducting heating gases across the bottom ofthe metal charge below the pier to first raise the temperature of thebottom of .the charge, then -"causing the heating gases to pass upwardlybetween said covers to raise the temperature of the top and sides of thecharge and finally venting the heating gases through the outer cover tothe atmosphere, the bottom of the charge being thus heated by conductionand the remainder of the charge by combined conduction and radiation,the charge being at all times maintained out of direct contact with saidheating gases. l t

4. A method of annealing as defined by claim wherein a thick metal plateis disposed upon the central portion of the sealing plate to provide asupport for a metal charge and to transmit heat received by the sealingplate to the bottom of said charge.

7. An annealing furnace as defined by claim 2 wherein the sealing plateis provided with troughlike portions in which the inner cover rests andin which a sealing medium is disposed.

8. A method of annealing as defined by claim 3 wherein the heating gasesoriginate as a plurality of distinct and substantially parallelgaseou'sstreams disposed along each side of the charge, the streams on one sideof the charge traveling initially in a. direction opposite to thestreams on the other side.

\9. In an annealing furnace of the character described, a refractorybase, a series of heating ducts passing in a generally horizontaldirection through such base and composed of material having a high rateof heat transfer and a metal sealing plate disposed upon said refractorybase and adapted to prevent the passage of air upwardly through saidbase due to the inherent porosity of the refractory material of thebase,

the said sealing plate being provided with trough- 35 shaped portionscorresponding to recesses in said base and having a relatively thickmetal plate disposed thereupon between said trough-shaped portions forsupporting and transmitting heat to JOHN R. TAYLOR.

a charge of metal adapted to be disposed there-

